Ask for certification of imported shared team key

A typical shared team key is a public primary key with one or more
secret subkeys. Therefore we skip asking for certification only if a
key with secret primary key was imported. Moreover, we need to improve
the check for the import of a single key because sometimes the import
result of a single key import contains multiple import objects.

(cherry picked from commit b333e895ef463fe04b7fb745eab1911357283e68)

• GnuPG-bug-id: T7502